There are two atrio-ventricular valves in the heart; one on the left side of the heart and one on the right side of the heart. The left side atrio-ventricular valve is the mitral valve and the right side atrio-ventricular valve is the tricuspid valve. Both of these valves are subject to damage that requires that the valve be repaired or replaced. Experience has shown that damaged valves can be surgically repaired, and that the long term results obtained from valve repair can be better than replacement of the valve.
The mitral and tricuspid valves differ significantly in anatomy. While the annulus of the mitral valve is generally D-shaped, the annulus of the tricuspid valve is more circular. The effects of the valvular dysfunction vary between the mitral valve and the tricuspid valve. Mitral valve regurgitation has more severe physiological consequences to the patient than does tricuspid valve regurgitation, a small amount of which is tolerable. In patients with valvular insufficiency, it is increasingly common surgical practice to retain the natural valves and to attempt to correct the defect. Many of these defects are associated with dilation of the valve annulus. This dilatation not only prevents competence of the valve, but also results in distortion of the normal shape of the valve orifice. Remodeling the valve annulus is therefore central to most reconstructive procedures for both the mitral and tricuspid valves.
Mitral or tricuspid valve annuloplasty is a restoration of the valve annulus, which effects full closure of the valve's leaflets by reestablishing the size and the shape of the normal mitral or tricuspid valve annulus. Surgical procedures such as annuloplasty more commonly incorporate the use of a prosthetic ring, where the ring is implanted over or within the mitral or tricuspid valve annulus.
In mitral valve insufficiency, the valve leaflets do not fully close and a certain amount of blood leaks back into the left atrium when the left ventricle contracts. As a result, the heart has to work harder by pumping not only the regular volume of the blood, but also the extra volume of blood that regurgitated back into the left atrium. The added workload creates an undue strain on the left ventricle. This strain can eventually wear out of the heart and result in morbidity when the conditions are prolonged and severe enough. Consequently, proper function of the mitral valve is critical to the pumping efficiency of the heart.
Many surgical procedures have been described to correct pathology of the valve leaflets, chordal tendineae, and, papillary muscles. In mitral valve repair, it is desirable to preserve the normal distance between the two fibrous trigones. The trigones more or less straddle the anterior leaflet portion of the mitral annulus. A significant surgical reduction of the inter-trigonal distance could cause left ventricular outflow tract obstruction. Thus, it is desirable to maintain the natural inter-trigonal distance after mitral valve surgery. Consequently, when a mitral valve is repaired, the result is generally a reduction in size of the posterior segment of the mitral valve annulus.
In a mitral valve repair, it is necessary to either diminish or constrict the involved segment of the mitral annulus so that the leaflets may coapt correctly when closing or, alternatively, to stabilize the annulus to prevent the possibility of dilatation from occurring. The latter is frequently achieved by implantation of a prosthetic ring in the supra-annular position. The purpose of the ring is to restrict and/or support the annulus to correct and/or prevent valvular insufficiency. However, it is important not to over-restrict the annulus or unacceptable valve stenosis could result.
As described above, in mitral valve repair, constriction of the mitral annulus should take place only in the area of the posterior portion of the native valve annulus. Shortening of the posterior portion of the mitral valve annulus may be accomplished by implanting an inexpansible rigid ring. With this approach, the surgeon must accurately choose the size of the ring that would prevent insufficiency, yet will not cause significant valve stenosis. A second approach uses a contractible ring that may be plicated during implantation. This approach has a disadvantage that a surgeon must accurately gauge not only the ring size to use, but also how to space the implanting sutures in the ring and the native annulus so that, when implanted, insufficiency is minimized. A third approach involves semi-expandable rings that may be contracted only in appropriate segments of the native annulus (but not in the anterior portion). The natural inter-trigonal distance should be maintained and the anterior leaflet should not be diminished in this circumstance.
In tricuspid valve repair, constriction of the annulus usually takes place in the posterior leaflet segment and in a small portion of the adjacent anterior leaflet. The septal leaflet segment is not usually required to be shortened.
Mitral and tricuspid valve disease is traditionally treated by surgical repair with an annuloplasty ring or surgical or replacement with a valve prosthesis. However, surgical valve replacement or repair is often an exacting operation that is done through a surgical technique where the thoracic cavity is opened. The operation requires use of a heart-lung machine for external circulation of the blood as the heart is stopped and opened during the surgical intervention and the artificial cardiac valves and/or annuloplasty rings are sewed in under direct vision. This operation exposes the patient to many risks especially in the elderly population. A percutaneous procedure that can be performed under local anesthesia in the cardiac catherization lab, rather than in cardiac surgery, could therefore offer tremendous benefits for these patients, many of whom have no options today. A minimally invasive surgical technique and percutaneous approach for delivering a prosthetic ring for mitral or tricuspid valve repair could be one of the most prominent tools in order to provide opportunities to treat patients with severe valvular insufficiency and/or end stage heart failure.